Thin-film magnetic discs or media are widely used as data storage media for digital computers. The discs are typically formed by successively sputtering onto a rigid disc substrate and underlayer, a magnetic recording layer and a carbon overcoat which protects the magnetic layer from wear and reduces the frictional forces between the disc and the read.thrfore.write head.
In addition to having excellent magnetic recording properties, for example, a high coercivity and low noise, it is highly desirable for the magnetic recording discs to be stable against oxidation of the magnetic layer. It is a recognized problem in the art that the surface of magnetic media are susceptible to moist atmospheric corrosion and that such corrosion to the surface causes a reduction in magnetic properties of the medium.
One approach for improving the stability of the magnetic medium has been to include chromium as a component in the alloy forming the magnetic recording layer, since chromium is known to offer corrosion resistance (Howard, U.S. Pat. No.
4,789,598; Natarajan U.S. Pat. No. 4,929,514).
Another approach to protecting the magnetic layer from wear and/or contamination, e.g., oxidation, has been to provide special layers or coatings over the magnetic layer. For example, Opfer (U.S. Pat. No. 4,631,202; EP 145157) describes a magnetic recording medium having a barrier layer disposed on a CoPt magnetic recording layer, the barrier layer having a thickness of between 100-600 .ANG.. Yanagisawa (U.S. Pat. Nos. 4,152,487 and 4,154,875) describes a magnetic medium having a 100-300 .ANG. protective layer made of a polysilicate and formed on the magnetic layer.
Such protective layers are also known in the field of tape-based magnetic media, where corrosion-resistant protective films deposited on the magnetic layer to prevent penetration of moisture and thus corrosion of the magnetic layer have been described. For example, Sato (U.S. Pat. No. 5,672,425) describes a protective layer selected from a group of metals and having a thickness of greater than 30 A.
One problem with the protective layers disclosed in the art is that the layer must be relatively thick to provide the desired protective properties. The disadvantage to a thick protective layer is the accompanying increase in distance between the magnetic layer and the transducer head, e.g., the flying height, which leads to increased spacing loss and limits the recording density of the disc and diminishes other recording properties, such as the signal amplitude.